A fluororesin has excellent characteristics such as weather resistance, fire retardancy, heat resistance, antifouling properties, smoothness and chemical resistance, and is suitable as a material of articles exposed to an outdoor environment. Among the fluororesins, vinylidene fluoride-based resins, in particular, polyvinylidene fluoride (hereinafter referred to as “PVDF”) has a large difference between a melting point and a decomposition temperature, and is a thermoplastic resin suitable for fabrication. However, the crystal of the PVDF tends to grow up to a size larger than wavelengths of visible light and scatters a part of the visible light, and accordingly the transparency becomes low. Because of this, it has been difficult to apply the PVDF to transparent materials.
Cases of the development of resin materials incorporating the properties of the PVDF have been reported in the past. For example, in Patent Literature 1, a block polymer formed of a block chain compatible with a vinylidene fluoride-based resin and a soft block chain is mixed with a vinylidene fluoride-based resin to reform the flexibility and impact strength of the vinylidene fluoride-based resin. In addition, in Patent Literature 2, an ABC triblock polymer is used to achieve both a thermal deformation temperature and impact performance of the crystalline resin. In any of the literatures, an acrylic-based resin (PMMA) is used as a compatible block with the vinylidene fluoride-based resin.
However, as for the mixture with these block polymers, there are many cases in which mechanical properties and thermal properties of the vinylidene fluoride-based resin are improved by the introduction of domains having different chemical properties, and there is no known example in which both of the transparency and the crystallinity are achieved by controlling the crystal size.
Example 1 of Patent Literature 2 discloses that the appearance becomes transparent by the mixture of the block polymer and the vinylidene fluoride-based resin. However, the specific transmittance is not referred to, and from the result of form observation by a transmission electron microscope, it is merely stated that the matrix is a PVDF+PMMA block mixture. In other words, the increase in the transparency in Example 1 of Patent Literature 2 is not caused by the refinement of the crystal size, but is caused by the decrease in the crystallinity itself.